Mycophenolate mofetil (MMF) is an immunosuppressive drug widely used in solid organ transplantation, and it may play an increasing role in autoimmune disease. MMF has been introduced as a novel immunosuppressive agent in systemic lupus erythematosus (SLE), often in patients intolerant of or resistant to conventional immunosuppressive regimens. We studied 21 patients with SLE, most of whom had previously received courses of cyclophosphamide therapy and had also received courses of azathioprine or methotrexate. Indications for treatment included uncontrolled disease activity and worsening renal involvement. MMF treatment resulted in reduced disease activity, as assessed by the SLEDAI (SLE disease activity index) (P=0.0001) and decreased proteinuria (P=0.027) while allowing a significant reduction in oral corticosteroid dose (P=0.0001). Levels of complement factors C3 and C4 and anti-double-stranded DNA antibodies were not significantly affected. MMF appears to be a safe and effective alternative immunosuppressant for extra-renal and renal disease in SLE not responding to conventional immunosuppressive treatment.